Your idea depends entirely on the HOA contract/covenants and the laws of the city and state. In many locations, you can refuse to pay, en masse, and you will be foreclosed upon, en masse. You may find sympathetic judges in some areas, but you're just as likely to find their hands tied in others.
Bottom line: If you don't like the contract, don't sign the contract. If you sign the contract, you're legally bound by the contract insofar as it doesn't violate local/state laws. If it does, your recourse is limited to those portions which violate the law.
That's just the way contracts work in the Western world, and covenants are stronger than mere contracts. They're lasting, binding agreements. By "lasting" I mean they outlast current owners; they're conveyed with the property. It's incumbent upon the buyer to research and know the covenants. If they're misrepresented by a realtor or the seller, then fiscal relief can be had from the realtor or the seller, but if the covenants were misrepresented, options such as keeping the treehouse up aren't on the table.
Railing against it will get you foreclosed. Rallying the other homeowners to your "cause" will get you foreclosed. Says so, right in the covenants.
Did you read them before you signed them?
